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H ave been trying to understand spectroscopic notation and have made some progress. However, when looking at the Spectral atlas of Arcturus I have come across notation I can't track down.

Examples are Q124*** , P240** and R132

I would be please to have any explanation or pointers to where to look these up as Google did not seem to help.

Thanks Andrew

PS I have spotted they are related to molecular lines but if anyone has a good reference that would be helpful.

Hi Andrew,
may be
C. R. Khitchin, Optical Astronomical Spectroscopy
will help. There is a section and list of other publications about molecular spectra. Google may help you under the keyword IR spectroscopy.

Cheers
Christian

Hi Andrew,
I think it's about molecular spectroscopy. The designations are typical for the P, Q and R- branches of a vibrational band. Take a look at Wikipedia under "Rotational-vibration Spectroscopy":

"...In the simplest cases the part of the infrared spectrum involving vibrational transitions with the same rotational quantum number (ΔJ = 0) in ground and excited states is called the Q-branch. On the high frequency side of the Q-branch the energy of rotational transitions is added to the energy of the vibrational transition. This is known as the R-branch of the spectrum for ΔJ = +1. The P-branch for ΔJ = −1 lies on the low wavenumber side of the Q branch. The appearance of the R-branch is very similar to the appearance of the pure rotation spectrum, and the P-branch appears as a nearly mirror image of the R-branch"

The number behind the letter P,Q,R indicates the associated rotational transition.

Kind regards
Klaus

Thanks both for your replies. I understand now and know where to look if I need more detail.

Regards Andrew